This research will examine the effectiveness of vitamin D or placebo (the placebo is a tablet that looks like Vitamin D study drug, but has no Vitamin D study drug in it), with and without physical activity (walking and progressive resistance exercise), in treating bone loss in women who have undergone treatment for breast cancer. The investigators would also like to find out if the physical activity program improves cardiovascular fitness, energy expenditure, muscular strength, muscle mass, and balance. One hundred five (105) subjects are expected to take part in this study. The investigators don't know if bone loss in breast cancer survivors should be treated differently than bone loss in other women.

To collect preliminary data on the effects of vitamin D therapy and exercise (alone or in combination) on bone metabolism biomarkers in non-metastatic breast cancer patients who began hormonal therapy within the previous 12 months.

To collect preliminary data on the effects of vitamin D therapy and exercise (alone or in combination) on bone mineral density (BMD) as measured by a dual energy X-ray absorptiometry (DXA) in non-metastatic breast cancer patients who began hormonal therapy within the previous 12 months.

Vitamin D3 50,000 IU: Patients will be assigned to receive a daily multivitamin, calcium supplement and 50,000 IU/week of vitamin D for a period of 24 weeks.

Drug: Vitamin D3

Vitamin D3 50,000 IU

Active Comparator: Vitamin D3 50,000 IU and Physical Activity

Vitamin D3 50,000 IU and Physical Activity: Patients will be assigned to receive a daily multivitamin, calcium supplement, 50,000 IU/week of vitamin D, and a progressive walking and resistance band exercise prescription for a period of 24 weeks.

Drug: Vitamin D3

Vitamin D3 50,000 IU

Behavioral: Physical Activity

Progressive walking and resistance band exercise prescription for a period of 24 weeks

Must have a functional capacity rating of ≤ 2 on the Eastern Cooperative Oncology Group (ECOG) performance status when assessed at baseline.132

Must have the approval of their treating physician (or physician's nurse practitioner or physician's assistant) to participate in sub-maximal physiological fitness testing and a low to moderate home-based walking and progressive resistance exercise program and to receive the 24-week supplementation of vitamin D.

Must be less than five years from the diagnosis of breast cancer and must be within 12 months of starting treatment with aromatase inhibitors (AI) in accordance with American Society of Clinical Oncology (ASCO) guidelines.

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To learn more about this study, you or your doctor may contact the study research staff using the Contacts provided below.
For general information, see Learn About Clinical Studies.

Please refer to this study by its ClinicalTrials.gov identifier: NCT01419730